I'm using rtl_fm in a scanning (nbfm) situation, and even with the antenna input disconnected and terminated, I get a burst of noise that sounds like a squelch tail maybe once each scan cycle.  They're a little over 1 second apart.  I've tried setting the squelch up to 10000 where I don't get signals anymore, but I still get the noise. I discovered that if you scan and have the output be a raw audio file, nothing gets recorded when nothing breaks squelch.  This makes time-lapse recordings where all the pauses are taken out.  Very nice, except for the noise bursts. I'm using: #!/bin/sh rtl_fm -N -S -l 132 -p 102 -f 854040000 -f 854240000 -f 854315000 -f 854415000 -f \ 854490000 -f 854540000 -f 855165000 -f 855240000 -f 858790000 -f 867350000 \ -f 867715000 /tmp/`date +"%Y-%m-%d_%H%M.raw"` and recorded overnight, but I mostly got noise bursts.   Alan ----- Radio Astronomy - the ultimate DX